Processing thermoplastics material

ABSTRACT

This invention relates to the preparation of plasticized thermoplastics material. The material, in particulate or strip form, is passed through the gap between the rolls of a rolling mill. A controlled amount of shearing work is performed on the material to effect uniform heating of the material. Coloring or filling matter may be passed between the rolls with the thermoplastics material to be homogeneously distributed, and reinforcing fibers may be placed between two layers of strip material passed between the rolls at the same time to become firmly embedded in the resultant single-layer strip.

0 iiriite States aterit Inventor Hugh Ford London, England App]. No.844,051 Filed July 23, 1969 Patented Jan. 4, 1972 Assignee Davy PlasticsMachinery Limited Poole, Dorset, England Priority July 23, 1968 GreatBritain 35005 PROCESSING THERMOPLASTICS MATERIAL 9 Claims, 2 DrawingFigs.

U.S. Cl 259/187, 259/189, 259/191 Int. Cl 132% 1/00 Field of Search 18/2EM; 259/6 [56] References Cited UNITED STATES PATENTS 2,645,813 7/1953Swallow 18/2 EM X 2,868,517 1/1959 Lasch 18/2 EM X PrimaryExaminer-Travis S. McGehee Attorney-Holcombe, Wetherill & BriseboisABSTRACT: This invention relates to the preparation of plasticizedtherrnoplastics material. The material, in particulate or strip form, ispassed through the gap between the rolls of a rolling mill. A controlledamount of shearing work is performed on the material to effect uniformheating of the material. Coloring or filling matter may be passedbetween the rolls with the thermoplastics material to be homogeneouslydistributed, and reinforcing fibers may be placed between two layers ofstrip material passed between the rolls at the same time to becomefirmly embedded in the resultant single-layer strip.

PATENTEB JAN 4:912

PROCESSING THERMOPLASTICS MATERIAL It is usual for Manufacturers ofthermoplastics material such as polyethylene, polypropylene,polyvinylchloride and like thermoplastics polymer material to extrudethe material into strip form and subsequently pelletise or otherwisedivide the strip of material into small parts before it is delivered tousers of the material. The users of the plastics material remelt thedivided material sufficiently for it to form a semisolid or liquid massimmediately prior to the material being used for forming plasticsarticles.

It is believed that it would be more convenient and possibly cheaper formanufactures of the plastics material not to divide the extruded stripinto small parts but to coil it and deliver the coils suitably protectedto the users of the material. The problem then exists of how the stripof plastics material can be melted prior to it being processed furtheror used for forming plastics articles. Advantageously, the solution tothis problem should also be applicable to the melting of thermoplasticsmaterial in the conventional pelletised form, so that the user is ableto process plastics materials supplied in either pelletised or stripform in the same way.

According to the present invention, there is provided a method ofprocessing thermoplastics material wherein the material is passedthrough the gap between at least one pair of closely spaced, processingrolls which perform sufficient mechanical work on the material to causeit to soften to a semisolid or liquid condition.

The invention also provides apparatus for processing thermoplasticsmaterial, comprising at least one pair of closely spaced processingrolls, means for driving at least one roll of said pair, means forfeeding the material into the gap between the rolls of said pair, andmeans for collecting processed material issuing from between the rollsof said pair.

In this specification, the term closely spaced is to be construed asmeaning spaced sufficiently close to provide the degree of mechanicalworking on the thermoplastics material to effect the required heating."It is well known that passing material through the gap between two rollscauses shearing within the material. For a given spacing between therolls, the extent of this shearing will depend on the size of thematerials supplied to the rolls, and the speeds of rotation of therolls. The required spacing, in any particular case, can be found bysimple experiment. For example, where a 0.5-inch gap between two 6-inchdiameter rolls rotating, respectively, at 180 rpm. and at rpm, thematerial is raised to a temperature of about 160 C. and issues frombetween the rolls in a semimolten condition. Variation in the extent ofmelting can be effected by altering:

a. the spacing between the rolls;

b. the thickness of the strip material; or

c. the diameters of the rolls,

or by making such an alteration in conjunction with an alteration in therelative speeds of the rolls.

In order that the invention may be properly understood two embodimentsof the apparatus according to the invention, and

their methods of operation, are described below, by way of example only,with reference to the accompanying drawing, in which:

FIG. I shows an arrangement of apparatus for treating a coil ofthermoplastics strip material; and

FIG. 2 shows a modification to part of the apparatus shown in FIGv 1.

As shown in FIG. 1, a coil 1 of thermoplastics strip material issupported for rotation in a cradle formed of freely rotatable, parallel,bearing rollers 2. The free end 3 of the coiled strip material passesover an idler roller 4 and into a rolling mill assembly 5.

The rolling mill assembly 5 consists of a rigid housing 6 encasing twopairs of rolls 7A, 7B and 8A, 83. One roll of each pair, 7A and 8A, ismounted in horizontally movable bearing blocks 9, and screw threadadjustment means 10 are provided for varying the gaps between the rollsof each pair. The pairs of rolls are also mounted so that there isalways a small clearance gap C between each of the rolls 7A and 7B ofone pair and the vertically adjacent roll 8A and 8B of the other pair.The housing cavity accommodating the rolls is open at the top and bottomfor supply and discharge of the plastics material, and the walls of thehousing cavity conform closely to the adjacent surfaces of the rolls.

Drive means 10 are independently and detachably connected to each of therolls by conventional means (not shown) for independently varying thespeed and direction of rotation of each roll. When the rolls 7A and 7Bare driven in opposite directions, as shown by the arrows in FIG. I, thespeed differential between these two rolls is adjusted as required andplastics strip material from the coil is fed through the gap between therolls 7A and 7B and issues into space 11 between the four rolls in asoftened condition.

Wedge-sectioned scrapers 12 are mounted adjacent the cylindricalsurfaces of rolls 7A and 7B and serve to remove plastics materialadhering to these rolls. The scrapers 12 are also arranged to help sealthe space 11 against egress of plastics material through the gaps Cbetween the rolls 7A and 8A and between the rolls 7B and 8B. Material inthe space II is therefore passed through the gap between the rolls 8Aand 8B and is collected in a gutter 13 for discharge through an outletopening 14.

In the apparatus shown in FIG. 1, rolls 7A and 8A are both driven in aclockwise direction and rolls 7B and 8B are both driven in ananticlockwise direction. The rolls 8A and 88 thus assist the scrapers 12in preventing egress of plastics material from the space 11 through theclearance gaps C as well as causing such additional shear in theplastics material as may be required for melting.

Sealing edges 15 projecting from the wall of the housing 6 on oppositesides of the gutter l3 bear against the cylindrical surface of the rolls8A and SE to prevent material issuing from between the rolls 8A and SEfrom being carried away from the gutter 13 on the surfaces of theserolls.

Each of the rolls 7A, 73, 8A and 8B is hollow and encloses ducts W(shown schematically in FIG. 1) for the circulation of heating orcooling water. Heating water is circulated where greater heating ofplastics material is required, and cooling water is circulated where thetemperature of the plastics material must be maintained below a certainlevel, for example, the temperature at which a plastics material such aspolyvinylchloride is degraded.

FIG. 2 shows part of an apparatus which is similar to that shown in FIG.1, but differs in that the gutter 13A is part circular rather thanrectangular in cross section, and an extrusion screw 14A is mounted inthe gutter 13A and extends into a conventional barrel (not shown)outside the housing. The outlet opening is thus formed coaxially aroundthe extruder screw 14A rather than at the bottom of the gutter. In allother respects the modified apparatus shown in FIG. 2 is the same asthat shown in FIG. 1, and the only difference in operation is thatplastics material is discharged horizontally from the apparatus by theextrusion screw 14A rather than vertically.

The softened plastics material discharged from the rolling mill assemblymay be transferred, for example, to a Banbury mixer for furtherprocessing or to the pressure section of an extruder, as in FIG. 2, orto a melt pump. However, by enclosing the rolls of the rolling millassembly 5 in a rigid housing, considerable pressure can be built-up onthe downstream side of the second pair of rolls 8A and 8B so as toobviate the need for an extruder.

As the speeds of the rolls of each pair may be varied relative to eachother and relative to the rate of feed of strip material, it may benecessary to roughen the surface of at least one of the rolls in orderto increase the rate at which the material is passed through the gapbetween the rolls.

Where the material fed into the gap between the rolls is in particulateor pelletised form a suitable hopper with an elongate discharge slotaligned with the gap between the rolls may be provided. Pellets are thusdropped through the hopper into gap between the rolls.

One advantage of the apparatus described above, over the conventionalextrusion plasticizer is that a more exact control of the shearing workput into the plastics material can be ensured, and closer control oftemperature is possible since the material passes through an exactlyspecified path while it is under deformation and pressure. Moreover,treatment of the material is more uniform and the material is softenedmore homogeneously.

The present invention may also be applied to the uniform distribution ofadditive material for coloring or filling the thermoplastics material,or for producing reinforced strips of thermoplastics material. In onesuch application, additive material is provided as a layer ofparticulate or film material on at least one of the rolls between whichthe thermoplastics material is passed. Where the thermoplastics materialis in strip form, one or more layers of strip material may be fed intothe gap between a pair of rolls at the same time and the additivematerial may be provided as a coating on at least one surface of onesuch layer, Where a plurality of layers of strip material are fed intothe gap between a pair of rolls at the same time, reinforcing fibers maybe provided on at least one surface of at least one of the layers sothat after passage between the rolls they become embedded in asingle-layer, composite strip.

I claim:

1. Apparatus for processing thermoplastics material comprising ahousing, a pair of rolls mounted for rotation in the housing, said rollsbeing arranged side by side with their longitudinal axes parallel in asubstantially horizontal plane and a clearance gap therebetween, aninlet in the housing positioned above said gap through whichthermoplastics material is introduced into the gap, means for causingrelative rotation between the rolls in such a direction that thesurfaces of said rolls adjacent said gap move so that materialintroduced into the gap is drawn through the gap to cause the materialto soften to a semisolid or liquid condition, the gap between the rollsleading to a recess within said housing beneath the rolls and into whichsaid softened material is forced by the action of the rolls, said recesshaving an outlet and being defined in part by a pair of scraper sealsacting against the underside of the rolls to prevent softenedthermoplastics material leaving the recess while adhering to the rolls.

2. Apparatus as claimed in claim 1 in which the outlet from said recessis defined by a clearance gap between a further pair of rolls mountedfor rotation in the housing, said further pair of rolls being arrangedside by side with their longitudinal axes parallel in a substantiallyhorizontal plane and a gap therebetween, said apparatus also comprisingmeans for causing relative rotation between the further rolls in such adirection that the surfaces of said further rolls adjacent the gaptherebetween move so that material introduced into the gap between saidfurther rolls from the recess is forced through that gap, a gutterpositioned beneath said last-mentioned gap, an outlet from said gutter,and a pair of scraper seals associated with the gutter and actingagainst the underside of the rolls to prevent softened thermoplasticsmaterial leaving the gutter while adhering to the rolls.

3. Apparatus as claimed in claim 2 including means for adl justing theposition of one roll of each pair relative to the other roll of the pairto vary the width of the gap therebetween.

4. Apparatus for processing a thermoplastics material comprising ahousing, a pair of rolls mounted for rotation in the housing, said rollsbeing arranged side by side with their longitudinal axes parallel and aclearance gap therebetween, an inlet in the housing positioned adjacentsaid gap through which thermoplastics material is introduced into thegap, means for causing relative rotation between the rolls in such adirection that the surfaces of said rolls adjacent said gap forcematerial introduced in the gap directly through the gap to cause thematerial to soften to a semisolid or liquid condition, the gap betweenthe rolls leading to a recess within said housing and into which saidsoftened materiai is forced by the action of the rolls, said recesshaving an outlet and being defined in part by a pair of scraper sealsacting against the rolls in the VlCH'llty of the gap to prevent softenedthermoplastics material leaving the recess while adhering to the rolls.

5. Apparatus according to claim 1, wherein drive means are independentlyand detachably connected to each of the rolls of said pair forindependently varying the speed and direction of rotation of the rollsof said pair.

6. Apparatus according to any of claim 1, wherein at least one roll ofsaid pair incorporates heat transfer means for con trolling thetemperature of said roll.

7. Apparatus according to claim 1, wherein the rolling surface of atleast one of the rolls of said pair is roughened so as to increase therate at which material is passed through the gap between the rolls ofsaid pair.

8. Apparatus according to claim 2, wherein the gutter is part circularin cross section and accommodates an extrusion screw for dischargingcollected thermoplastics material through an aperture coaxially alignedwith the extrusion screw.

9. Apparatus according to claim 1, wherein said means for feedingmaterial into the gap between said pair of rolls comprises a hopper forparticulate thermoplastics material which has an elongate discharge slotaligned with said gap.

1. Apparatus for processing thermoplastics material comprising ahousing, a pair of rolls mounted for rotation in the housing, said rollsbeing arranged side by side with their longitudinal axes parallel in asubstantially horizontal plane and a clearance gap therebetween, aninlet in the housing positioned above said gap through whichthermoplastics material is introduced into the gap, means for causingrelative rotation between the rolls in such a direction that thesurfaces of said rolls adjacent said gap move so that materialintroduced into the gap is drawn through the gap to cause the materialto soften to a semisolid or liquid condition, the gap between the rollsleading to a recess within said housing beneath the rolls and into whichsaid softened material is forced by the action of the rolls, said recesshaving an outlet and being defined in part by a pair of scraper sealsacting against the underside of the rolls to prevent softenedthermoplastics material leaving the recess while adhering to the rolls.2. Apparatus as claimed in claim 1 in which the outlet from said recessis defined by a clearance gap betweeN a further pair of rolls mountedfor rotation in the housing, said further pair of rolls being arrangedside by side with their longitudinal axes parallel in a substantiallyhorizontal plane and a gap therebetween, said apparatus also comprisingmeans for causing relative rotation between the further rolls in such adirection that the surfaces of said further rolls adjacent the gaptherebetween move so that material introduced into the gap between saidfurther rolls from the recess is forced through that gap, a gutterpositioned beneath said last-mentioned gap, an outlet from said gutter,and a pair of scraper seals associated with the gutter and actingagainst the underside of the rolls to prevent softened thermoplasticsmaterial leaving the gutter while adhering to the rolls.
 3. Apparatus asclaimed in claim 2 including means for adjusting the position of oneroll of each pair relative to the other roll of the pair to vary thewidth of the gap therebetween.
 4. Apparatus for processing athermoplastics material comprising a housing, a pair of rolls mountedfor rotation in the housing, said rolls being arranged side by side withtheir longitudinal axes parallel and a clearance gap therebetween, aninlet in the housing positioned adjacent said gap through whichthermoplastics material is introduced into the gap, means for causingrelative rotation between the rolls in such a direction that thesurfaces of said rolls adjacent said gap force material introduced inthe gap directly through the gap to cause the material to soften to asemisolid or liquid condition, the gap between the rolls leading to arecess within said housing and into which said softened material isforced by the action of the rolls, said recess having an outlet andbeing defined in part by a pair of scraper seals acting against therolls in the vicinity of the gap to prevent softened thermoplasticsmaterial leaving the recess while adhering to the rolls.
 5. Apparatusaccording to claim 1, wherein drive means are independently anddetachably connected to each of the rolls of said pair for independentlyvarying the speed and direction of rotation of the rolls of said pair.6. Apparatus according to any of claim 1, wherein at least one roll ofsaid pair incorporates heat transfer means for controlling thetemperature of said roll.
 7. Apparatus according to claim 1, wherein therolling surface of at least one of the rolls of said pair is roughenedso as to increase the rate at which material is passed through the gapbetween the rolls of said pair.
 8. Apparatus according to claim 2,wherein the gutter is part circular in cross section and accommodates anextrusion screw for discharging collected thermoplastics materialthrough an aperture coaxially aligned with the extrusion screw. 9.Apparatus according to claim 1, wherein said means for feeding materialinto the gap between said pair of rolls comprises a hopper forparticulate thermoplastics material which has an elongate discharge slotaligned with said gap.